Rustless iron



Patented Mar. 21, 1939 UNITED STATES PATENT OFFICE" No Drawing. Application February L 1938, Serial No. 188,186

Claims.

This application is a continuation in part of my copending application, Serial No. 33,413, filed July 26, 1935, and entitled Rustless iron and the invention relates to an alloy iron and to corro 5 sion-resistant products or articles of manufacture of the same.

Among the objects of my invention is the provision of plates, sheets, wires, strips, bars and tubes, as well as special shapes, corrugated sheet, welded pipe and a variety of die, sand and centrifugal castings which are strong, tough and durable; which are resistant to the progressive corrosion under the various conditions encountered in actual, practical use with a minimum of special preparation of a corrosion-resisting surface, as by special heat-treatment, working or finishing; which may be riveted, welded, or otherwise fabricated into a variety of articles, structures, appliances or pieces of equipment.

invention it may be noted that the ordinary austenitic high-chromium, high-nickel stainless irons and steels containing as a rule from 16% to 20% chromium and from 7% to 12% nickel are subject to relatively rapid work-hardening at all temperatures below about 1600 F. and especially at room temperature. After welding they are prone to exhibit a phenomenon known as Weld decay when subjected to a wide variety of corrosive environments. Relatively rapid work-hardening and tendency toward weld decay both seriously hamper the commercial application of the abovementioned ordinary austenitic chromium-nickel alloys especially where ease of mechanical formability and of fabrication by welding are desired.

I have discovered that disadvantages noted may be overcome in the austenitic stainless irons or steels by maintaining the nitrogen and carbon contents at certain exceedingly low values. The absence of appreciable nitrogen and carbon in these austenitic alloys not only greatly decreases the rate of work-hardening and retards somewhat the occurrence of weld decay, as described above, but also contributes a slightly lowered minimum hardness to the fully annealed product. This property of lower hardness as such contributes further to ease of formability by mechanical operations.

I have found that a maximum degree of softness of annealed metal, a minimum rate of workheardening, and a retardation of the weld-decay phenomenon all are realized in the chromiumnickel austenitic steel alloys by maintaining a nitrogen content of .005 to .035 per cent and a carbon content of -.02 to .07 per cent. Best re- As conducive to a clearer understanding of my sults are had in such alloys where the nitrogen content of the alloy is less than .025 per cent and the carbon content is less than .05 per cent.

In accordance with the practice of my invention a heat of alloy iron, analyzing approximately 9% to 30% chromium, preferably 16% to 20% chromium, 5% to 15% nickel, preferably 7% to 12% nickel, .02% to .07% carbon, and .005% to .035% nitrogen, with the usual percentages of manganese, silicon, sulphur, and phosphorus and the balance substantially iron, is produced, for example in a manner particularly described in my recently granted U. S. Patent 1,945,400 en titled Process of making rustless iron. While a carbon content of .0'7% and a nitrogen content of 035% is permissible, it is decidedly preferable to conduct the melting operation so as to achieve as low a content of these ingredients as is commercially feasible. nitrogen in themetal is not desired; it is commercially unavoidable. Where such low values are reached, however, there is very little objection to their presence. Ordinarily the carbon content in the finished metal amounts to less than about 05% and. the nitrogen content less than about 025%, the total contents of the carbon and nitrogen then amounting to less than about .075%.

The products of my invention are strong, tough and ductile and may be readily formed as by deepdrawing, spinning, beading and upsetting into desired shapes. Furthermore, these products may be welded with a minimum of time and expense. Because of their low nitrogen and low carbon contents they possess a maximum stability of austenite for any selected percentage of chromium and of nickel contents which can be obtained without the presence of special stabilizing elements. Consequently I find it often permissible to omit annealing treatment after high-temperature working or welding.

These products of manufacture are peculiarly resistant to atmospheric attack under a wide variety of weather conditions, such as the summer heat, rain, the formation of ice on the products, and the like, all in the presence of dirt and dust contained in the atmosphere, and various salt, acidic or other corrosion-fostering agents commonly found in the air abdut industrial localities. Furthermore, these products are resistant to the attack of a great number of common acids, alkalies, and salts. In addition, the products are well adapted to withstand the shock and vibration and the various stresses of tension, compression and torsion from high-summer heat to sub-zero The presence of carbon and winter cold, as encountered in use, with excellent resistance to fatigue or failure.

Good results in electric and org-acetylene welding are achieved where a welding rod of an austenitic chromium-nickeliron or steel is employed.

For example, in welding products or the character indicated, good results are produced employing a rod of .07% or lower carbon content and analyzing at. least 1% higher in chromium than the parent metal; and containing nickel in as high or a higher percentage than the parent metal. The bead of metal is soft and because of its softness and high ductility the localization of welding stresses is minimized or rendered negligible. It will be understood, of course, that a welding rod may be used having the same composition as the material welded;

A soft ductile weld free of strain and embrittlement is assured by carefully conducting the welding operation in accordance with known methods so as to minimize the taking up of nitrogen by the weld metal. The presence of an appreciable nitrogen content in the weld bead and metal'adjoining the bead serves to give a higher inherent hardness and at the same time welding stresses and strains of greater magnitude, just as does the presence of an appreciable amount of carbon. By skillful operation of electric arc welding equipment or oxy-acetylene welding equipment nitrogen contamination of the 'weld is largely-avoided. 1 v

.Afte'r'the welding operation is complete in the fabrication of a desired structure, piece of apparatus or piece of equipment, the fabricated structure, as desired, may be annealed by uniformly reheating in a suitable furnace and then permit-.

ting to cool. The effect of such an annealing treatment is to achieve uniformity and stability of the resulting a'ustenite structure and to produce a maximum softness,'thereby relieving any vestiges of strain in the weld. The'low nitrogen and carbon contents of the metal are responsible for the above-mentioned highly desirable char,

acteristics. Moreover, both the weld metal itself and the parent metal possess the highly desirable property of a low rate of work-hardening already I mentioned above.

My alloy iron, plate, sheet, strip, bars, rods, wire, special shapes and tubes represent an excellent balance between a desired low manufacturing cost and good physical characteristics, such as extrememalleability, low yield strength, low

rate of work-hardening, and excellent adaptability to forming and welding operations.

about .3% .to 3%.

Zbars,1rods, wire and tubes in that this addition I reduces the susceptibility of these products to a peculiar type of local corrosive attack known as pitting. The molybdenum addition is particularly'desirablein products intended for marine duty where the corrosive attack of salt water and salt. spray'is encountered, as well as for resist ance, to sulphite liquors such as those encountered in the paper, textile and plastics industries. In

addition, molybdenumv in the amount indicated is advantageous-in lendingfa" certain solidity or soundness to the structure of the metal in. which;

it is included.

pp r n -moimts'fromabOut 20m, 1% or even 2% maybe present in the above products without detriment and indeed it may be advantageous for enhancing resistance to certain re-' ducing acids.

Silicon from about .5% to 2% or more increases the scaling resistance of the alloy at high temperatures. However, the presence of silicon above about 50% or even. about .35% tends to affect the rate of work-hardening unfavorably, that is to say to increase said rate, with a corresponding decreased ease of formability.

Where certain of the hot-rolled alloy iron plates, sheet, strip, bars and rods are to be machined considerably, any one of the ingredients,'sulphur, phosphorus, or-seleniurn, 'is preferably incorpo: rated in the alloy in any amount from about .08% to about .50%. Even when these special ingredients are added to confer improved machinability upon the alloy, ease of forming or formability is still retained to such a degree that coldupsetting and cold-heading operations may be performed thereon successfully.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiment hereinbefore set forth it will be understood that all matter described herein is to be interpreted as illustrative and not in 'a limiting sense.

I claim: I

1. In a composition of matter of the class described, a corrosion-resisting alloy iron of good ductility, formability and weldability which is of improved stability and unsubstantially hardenable, said alloy iron comprising approximately, 9 per cent to 30 per cent chromium, 5 per cent to 15 per cent nickel, .005 per cent to .035 per cent nitrogen, .02 per cent to .07 per cent carbon, and the balance consisting of iron.

2. In a composition of matter of the class described, a corrosion-resisting alloy iron of good ductility, formability and weldability which is of improved stability and unsubsta ntially hardenable, said alloy iron comprising approximately, 16 per cent to 20 per cent chromium, '7 per cent to 12 per cent nickel, .005 per cent to .035 per cent nitrogen, .02 per cent'to .07 per cent carbon' and the balance consisting of iron.

3. In articles of manufacture of the class described, corrosion-resisting plate, sheet and strip of good' ductility, formability and weldability, which is of improved stability, said plate, sheet and'strip comprising approximately, 9 per cent to 30 per cent chromium, 5 percent to 15 per cent nickel, .005 per cent to .025 per cent'nitrogen, .02 per cent to .05 per cent carbon and the balance consisting of iron.

4. In articles of manufacture of. the'class described, corrosion-resisting bars, rods and wire of good ductility, formability and weldability, which is of improvedstability, said bars, rods and wire comprising -approximately, 9 per cent to 30 per cent chromium, 5 per cent to 15 per cent nickel, .005- per cent to .025 per cent nitrogen, .02 per cent to .05 per cent carbon, and the balance consisting of iron.

5. In articles of manufacture of the class described, a welded corrosion-resisting alloy iron or steel product of improved stability and substantially hardened, comprising approximatelyfQ per centto 30 per cent chromium, 5'per cent to 15' percent nickel, .005 per centto .035 per cent with the balance consisting' of iron.

. WILLIAM-BELL amass. I

nitrogen, .02 percent to' .07 per cent carbon, 

